Tool set type powder compacting press

Abstract: A tool set type powder compacting press is proposed which is simple in construction and reliable. The driving shafts coupled through coupling shafts with the tool holding plates, that is, the punch plates are provided at the press side. Further, coupling means having removable joints is provided between the driving shafts and the punch plates. No driving means is provided at the tool set side. Since the driving mechanisms are integrated at the press side, the whole arrangement will have a simple construction. This will also increase the reliability.

Description: This invention relates to a powder compacting press which uses tool sets to manufacture powder compacts such as sintered parts. With a powder compacting press, a plurality of tools (including a die, a core and punches) are used to make a compact with a complicated shape having two or more steps. In the tool sets, a plurality of tools are mounted on respective tool holding plates. The tool holding plates are guided by guide rods to keep parallel to one another. Some of the tools are operated by driving mechanisms such as a cylinder attached to the tool holding plates or by mechanical interlocking mechanisms. From GB-A-2 025 834 there is known a powder compaction press which comprises a matrix holder plate, one or more punch holder plates and a core holder rod. This press further comprises a system of upper punch holder and means for the controlled displacement of said elements during the phases of compression, extraction of the moulding and return to the position for filling of the die cavity. In order to increase the rate of operation of the press, it is a general practice to provide a plurality of tool sets on a single press. Therefor, driving mechanisms have to be provided as many as the tool sets. When changing the setup, it is necessary to couple the driving mechanisms to a hydraulic, pneumatic or electric power source and connect signals. Also, the operation control mechanism and the tool position adjusting mechanism have to be attached to each tool set. This will increase the cost of tool sets and the time used to couple the driving source and the signals. Further, there is a problem that between a plurality of tool sets there is a difference in function with respect to one another. It is an object of the present invention to provide a tool set type powder compacting press which obviates this problem. According to the present invention, there is provided a tool set type powder compacting press with the features of claim 1. No adjusting mechanism for operation or positioning is provided at the tool set side. Therefore, controls of speed, position and power by means of electric or hydraulic servo control, by hydraulic/pneumatic pressure control or by other control are carried out only for the driving shafts. If there is a play or rattling at the connection between the tool holding plate of the tool set and the driving shaft in the press, it may unduly affect the quality of the products. Clamp mechanisms may be provided so that the joint portions for coupling can move in the axial direction to eliminate the gap between the joint portions. The operation of the tool holding plates in the tool sets is controlled by hydraulic/pneumatic pressure control or by electric/hydraulic numerical servo control. Also, mechanical means such as a hydraulic or pneumatic cylinder or a ball screw is generally used as a driving mechanism. However, such mechanisms include many factors that might give a bad effect on the control accuracy, such as internal leakages of hydraulic/pneumatic pressure, differences in the frictional resistances and in dimensional accuracies among the components in these mechanisms. Therefore, if the driving mechanisms are provided at the tool set side, there will be differences in the control accuracy among a plurality of tool sets. This unduly affects the quality of products. More specifically, the acceleration in the early phase of operation will vary due to the differences in sliding resistances in the cylinder rams and the differences in the internal fluid leakage. These differences in control accuracy will create differences in the compacting density in the products and may develop cracks. Furthermore, they will affect maintenance and durability with prolonged use. The more the number of the tool sets, the greater the bad effects. In the press according to the present invention, driving shafts are provided for the tool holding plates at the press side. Thus, the factors which create differences in control accuracy are reduced to minimum, thereby reducing bad effect on control accuracy. Usually, the adjusting mechanisms for controlling the operation and the position of the driving mechanisms are provided on the driving mechanisms. However, in the present invention, since no driving mechanism is provided at the tool set side, the number of adjusting mechanisms needed is fewer. Furthermore, if the tool holding plates in the tool sets and the rams in the press are coupled by means of joints, it is necessary to provide a gap therebetween to facilitate the fitting. This gap is usually between 0.05 - 0.1 mm, which is not negligible because it might delay the operation of the tool holding plate and decrease the accuracy in positioning for the tools. In the arrangement in which the clamp mechanism is provided on the coupling means, the gap can be reduced to zero, ensuring highly accurate compacting. The force applied by the clamp mechanism to the joint in the axial direction has to be set to be not less than the force applied to the clamp during operation. According to the present invention, since the functions are integrated at the press side, the tool sets will have a simple function. Thus, the following effects can be attained. (1) While using a plurality of tool sets on a single press, there are no difference in function between tool sets. Therefore, compacting can be done under the same conditions with high reproducibility. This increases the quality of the powder compacts. (2) Since the tool sets and the press are coupled only mechanically, neither electric or hydraulic/pneumatic pressure coupling is necessary. This makes it possible to reduce the time for setup. (3) Troubles such as short circuits, wire breakage, which are usually caused by powder materials attached to the electric connectors, contaminations of cylinder oil by powder material can be avoided. A more reliable system can be achieved. (4) Since the tool sets are simple in structure, it becomes possible to reduce the manufacturing cost and the equipment cost as a whole. Further, a larger number of tool sets can be mounted with the same equipment cost. It becomes easier to respond to smaller manufacturing lots. (5) No rattling will occur in the clamp mechanisms disposed in the coupling portions of the driving shaft of the press and the tool holding plate. Therefore, the powder compacts will have a higher quality. (6) The guide arm are mounted in the T-joint for coupling. The driving shaft does not have to be positioned to the coupling position. Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: Fig. 1 is a partially cutaway front view of one embodiment of the tool set type powder compacting press according to the present invention; Fig. 2A is a perspective view of a joint used in the coupling means; Fig. 2B is a front view of the same showing how it is connected; Fig. 3A is a sectional view of the clamp mechanism of the joint in its unclamped state; and Fig. 3B is a sectional view of the same in its clamped state. Fig. 1 shows an embodiment according to the present invention in which a tool set comprises tool holding plates, that is, punch plates 1a - 1f and a core rod 1g. Each punch and core rod is secured to the respective punch plate by use of an adapter. Also, in order to keep the punch plates 1a - 1f parallel one with another, they are guided by guide rods 2 so as to be movable relative to one another in the axial direction. Coupling shafts 3a - 3g are secured to the punch plates 1a - 1f and the core rod 1g on either top or bottom end thereof. These coupling shafts 3a - 3g are coupled to respective driving shafts 5a - 5g extending from the press. In Fig. 1, there is illustrated a tool set coupled to the press and comprising the upper punch plates 1a - 1c, the lower punch plates 1d - 1f, a die plate 4, and the core rod 1g. The number of the plates depends upon the number of the steps which the powder compact to be formed has. The coupling shafts 3a - 3g are coupled to the driving shaft 5a - 5g provided near the press, respectively, by joints shown in Fig. 2, each comprising a T-groove 6 and a T-joint 7. The dimensions of the T-groove 6 and T-joint 7 should be determined so that the T-joint 7 can be inserted in the T-groove 7 without any difficulty. The clearance should generally be 0.05 - 0.1 mm as mentioned above. It is not necessary for the compacting process, but it may affect the movement of the tools unduly and produce defects on the powder compact, which are; (i) While filling powder therein, the upper surface of the lower punch gets out of the position due to the clearance. As a result, the amount of the powder is subject to change, causing the weights and densities of the individual powder compacts to vary. (ii) The clearance decreases the precision of fine adjustment needed to compensate the deflection of punches. Therefore, cracks may develop in the compacts due to insufficient compensation of punch deflection. In order to avoid the abovesaid problems, in the device shown in the figure, a clamp mechanism 9 employing a clamp cylinder 10 shown in Fig. 3 is provided for each of the coupling portions between the coupling shafts 3d - 3f and the driving shafts 5d - 5f, respectively. A spring pushes up a piston rod in the clamp cylinder 10. The piston rod is pushed down by the fluid pressure so that the T-joint 7 integral with the piston rod will pull down the coupling shaft 3e - 3g. This will reduce to zero the clearance in the coupling portion in the axial direction and obviate the problem. The clamp force produced by the clamp cylinder 10 is set to be larger than the force resisting to the clamp mechanism while the press operates. As shown in Fig. 2A, it is preferable to provide a guide arm 8 at the head portion of the T-groove 7 so as to protrude diametrically therefrom. The width of the guide arm 8 is set to be narrower than that of the opening of the T-groove 6. As shown in Fig. 2B, the driving shaft is moved forward at low pressure with the guide arm 8 in contact with the bottom face of the T-groove 6. Thereafter, by moving the coupling shaft laterally, the driving shaft and the coupling shaft can be coupled easily without pre-positioning. In the above arrangement, the clamp cylinder can stroke freely. Even if the contact surfaces of the T-groove 6 and the T-joint 7 are not perfectly flat or parallel to each other, it can be compensated by the elastic deformation due to the clamp force. There is no problem in practical use. The T-groove 6 and the T-joint 7 can be brought into contact with each other perfectly since their flatness can be compensated by the elastic deformation. Thus, the wear caused by lapse of time in the contact surfaces will not raise any serious problem. The driving shafts provided at the press are controlled by the control mechanisms which are all provided in the press. In Fig. 1, scales needed to control each of the cylinders which actuate the driving shafts at the press are also provided in the press. All of the operation/position adjusting mechanisms except the one for adjusting the pressure position for each punch are provided in the press. Only the adjusting mechanism for pressure position for each punch is provided in the tool set. When the driving shafts have enough power to support the punches at the pressing position, these adjusting mechanisms in the tool set may not be necessary.

Claims: A tool set type powder compacting press for use with a tool set including an upper punch (1a - 1c), a lower punch (1d - 1f) and a die (4), at least one of said upper punch (1a - 1c) and said lower punch (1d - 1f) comprising a plurality of tools, said tool set further comprising tool holding plates which are as many as said tools and hold said respective tools, wherein said press is provided with driving shafts (5a - 5g) for operating said respective tool holding plates, said driving shafts (5a - 5g) being provided with means for controlling the operation and position of said tool holding plates and wherein coupling means for coupling said driving shafts (5a - 5g) with said tool holding plates is provided, characterized in that said driving shaft (5a - 5g) comprises a numerical servo control system. A tool set type powder compacting press as claimed in claim 1 wherein said coupling means comprises a clamp (9) which imparts an axial force to said joint to eliminate any gap between said driving shaft (5a - 5g) and said tool holding plate. A tool set type powder compacting press as claimed in claim 1 or 2 wherein said joint comprises a T-joint (7) adapted to fit in a T-groove (6).

Inventors: HORIE YOSHIAKI, SEI HIROMOTO, TAKEUCHI KENJI, HORIE, YOSHIAKI, SEI, HIROMOTO, TAKEUCHI, KENJI                                  ., HORIE, YOSHIAKI, C/O KOHTAKI PRECISION, SEI, HIROMOTO, C/O KOHTAKI PRECISION, TAKEUCHI, KENJI, C/O ITAMI WORKS OF SUMITOMO ELEC.
Applicants: KOHTAKI PRECISION MACH CO LTD, SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, INC.
Application year: 1994
Main classification: B30B11
IPC codes: B30B11, B30B15